Locking apparatus for a string

ABSTRACT

PCT No. PCT/NL93/00007 Sec. 371 Date Sep. 7, 1994 Sec. 102(e) Date Sep. 7, 1994 PCT Filed Jan. 8, 1993 PCT Pub. No. WO93/14489 PCT Pub. Date Jul. 22, 1993.A locking apparatus (1) for a string of a stringed instrument, which locking apparatus includes a locking cam (20, 23-27) arranged rotatably about a point of rotation and a locking wall, which locking cam and locking wall are positioned relative to each other in such a way that a string can be locked between them. The rotatably arranged cam is an eccentric made from a hard and stiff material, placed in a U-shaped channel of a hard and stiff beam (3). This channel contains the locking wall. A small spring holds the locking cam to the locking wall in case no string is present between the locking wall and the locking cam. The eccentric is shaped in such a way that the locking cam and the locking wall contact at only one point, in case there is no string between them.

FIELD OF INVENTION

The invention relates to a locking apparatus for a string of a stringedinstrument, which also includes a tuning mechanism for the string, whichlocking apparatus includes a locking cam arranged rotatably about apoint of rotation and a locking wall, which locking cam and locking wallare positioned relative to each other in such a way, that a string canbe locked between them.

BACKGROUND OF THE INVENTION

Such a locking apparatus for a string of for instance a violin or aguitar is known from U.S. Pat. No. 1,732,172. This known apparatuscomposes a joint construction with means to tune the individual stringsof the stringed instrument. Therefore, the string is guided through anopening in a channel of a tuning means. In order to anchor the string tothe stringed instrument the string is subsequently pulled out of theother side of the tuning means. Subsequently, the string is anchored tothe locking means. The locking apparatus includes a rotatably arrangedlocking cam and a locking wall, between which the end of a string can beguided. Both the locking cam and the locking wall in the knownapparatus, preferably, include a toughened surface. The locking cam andthe locking wall are shaped in such a way, that, when the string isbeing pulled in the direction of the other end of the string, thelocking cam and the locking wall seize and lock the string. Thereby thetensioned string is in direct physical contact with the locking cam oversuch an extent of the locking cam that the tension of the stringprovides for a leverage to the rotatably arranged locking cam andincreases the locking force of the locking apparatus. In order to usethe tuning means, the locking apparatus has to be guided into thechannel of the tuning means, while the string remains tensioned. Afterthe string is anchored on its other end, the locking apparatus can bemoved through the channel of the tuning means by means of a butterflynut, in order to regulate the tension in the spring.

In the known locking apparatus the locking cam is not provided with aspring, so that the locking cam, whenever no tensioned spring isinserted, will dangle without taking any defined position. Moreover,when a loose string is guided between the locking cam and the lockingwall, the string will not yet be locked. The will only remain lockedtight in the locking apparatus when the string is tensioned. Byinsertion of the string into the locking apparatus in the channel of thetuning means, therefore, the string has to maintain a certain tension,otherwise the string may still slip from the locking apparatus. In casethe string as yet slips loose, the whole procedure has to be repeated,which consumes a lot of time. When, for instance during a concert, astring breaks the known apparatus is very unpractical, since changing astring takes a lot of time. This is certainly true, when the stringslips loose from the locking apparatus in between. This known apparatustherefore is more suitable for violins, where the strings have a lowertension and are made of a rougher material than strings for a steelstring guitar.

The object of the locking apparatus according to the present inventionis to solve the problems mentioned above.

SUMMARY OF THE INVENTION

Therefore, the locking apparatus according to the invention ischaracterized in that the rotatably arranged locking cam is an eccentricfrom a hard and stiff material, placed inside a U-shaped channel beingfreely accessible from one side and provided in a hard and stiff beam,which channel includes the locking wall, a small spring being providedholding the locking cam to the locking wall in case no string is presentbetween the locking cam and the locking wall, and the eccentric isshaped in such a way that the locking cam and locking wall contact atonly one point in case there is no string in the channel.

By using a U-shaped, hard and stiff channel in combination with a hardand stiff eccentric which is pushed or pulled towards the locking wallin the channel by means of a spring, a locking apparatus of high qualityresults, with which the string can be locked most tightly, and withwhich the string can consequently be tensioned to a very high tension.This locking apparatus can be applied at one end of the string, whilethe tuning means is on the other side of the string. Therefore, thislocking apparatus is highly suitable for use together with a tremoloapparatus, in which the tuning means for a string is placed. The U-shapeof the channel makes the channel easily accessible for a string to beanchored, so that a broken string can be substituted quickly and easilyduring a concert. By providing the locking cam with a small spring, thestring will also remain locked in the locking apparatus in case thestring tension is strongly decreased. This, for instance, happens whenthe stringed instrument is provided with six strings that are anchoredat one side to a tremolo, which tremolo is activated after breakage ofone of the strings to release the tension from the remaining strings inorder to attach a new string. The springs hold the five strings, whichare then unloaded for a short period of time, in their original positionin the locking apparatus, so that they do not need to be tuned again,after the tremolo has returned to its neutral position.

It may be noted that from FIG. 5 from the prior art the application ofan eccentric is known. However, this is used in combination with asecond eccentric, which is placed mirrorwise opposite to the firsteccentric. Both eccentrics can rotate about their own axis, and can locka string in between them. Here also counts, that the string is onlylocked, when a certain tension is applied to the string. If not, thenthe string will slip loose from between the two eccentrics which are notprovided with springs and consequently have no initial locking load andno well defined initial position. As with the above mentioned knownlocking apparatus this locking apparatus is problematic when it has tobe inserted in the channel of the tuning means, because in thatsituation the string has to remain loaded with a certain tension inorder to prevent it from slipping loose from the locking apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will further be explained with reference to the drawings,which only serve as an illustration and not as a restriction of the ideaof the invention.

In the drawing:

FIG. 1 shows a locking apparatus according to the invention for a totalof six strings;

FIG. 2 shows a cross section through the locking apparatus according toFIG. 1;

FIG. 3 shows a top view of the locking cam according to the invention;

FIG. 4 shows a bottom view of the locking apparatus according to FIG. 1;

FIGS. 5 and 6 show two locking cams having different dimensions;

FIG. 7 shows a graph showing the relation between the locking force onthe string and the tension in the string;

FIG. 8 shows a perspective view of the locking apparatus attached to theneck of a guitar.

FIGS. 9 and 10 show a locking apparatus provided with a special springdesign of the locking cams;

FIGS. 11 and 12 show another embodiment of the locking apparatus.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 a locking apparatus 1 according to the invention is shown as abeam 3 provided with six U-shaped channels. Each channel is destined tohold one string. Of course the invention is not restricted to a beam 3having six channels; the invention also relates to beams with n U-shapedchannels, with n≧1. In each channel a locking cam 20, 23-37 is located,having the shape of an eccentric and provided with a turning point 21that fits into and interacts with a rotation cavity 5 placed in theinside walls 42-47 of each channel. Inside each U-shaped beam, the wallopposite to the wall provided with the rotation cavity 5 comprises alocking wall (for instance 411 in FIG. 2). Each locking cam is providedwith an opening 22 through the locking cam. A spring can be placed inopening 22, in such a way that the locking cam is pushed or pulledagainst the locking wall in case there is no string present between thelocking wall and the locking cam. In practice, the top of the beam doesnot provide enough space for such a spring 30. Therefore, beam 3 isprovided, inside each channel, with slots 31, so that the springs 30 canbe attached underneath the locking cams 20, 23-27 at the bottom side ofbeam 3. The springs can be attached more or less floating, as shown inthe drawing. It is also possible to insert a bolt or axle (not shown) toeach spring 30, around which the spring 30 can rotate.

Other designs for spring 31 are also possible, as shown in FIGS. 9 and10. Here, the locking cam 20 is provided with an axle 60, that rotatestogether with the locking cam 20 and is inserted in an opening 61through beam 3. At the bottom side of the beam axle 60 is connected toa, preferably plastic, retainer 62, in such a way, that the plasticretainer 62 follows every rotation of locking cam 20. A spring 63 isconnected to the plastic retainer 62, in such a way that in the initialposition locking cam 20 is pushed against the locking wall 411. Anappropriate cavity for plastic retainer 62 and spring 63 may be providedat the bottom side of beam 3, so that they do not protrude from the beam3. In the preferred embodiment according to FIG. 9, similar springdesigns are provided for the remaining locking cams 23-27. An advantageof the spring design 60-63 is, that it is easier to assemble than springconstruction 30-31 according to FIG. 2. FIG. 10 shows a cross sectionalong line X--X of FIG. 9.

Between the locking wall 411 and the locking cam 20 a string isinstalled by sliding the string along the bevelled edge 412 of lockingwall 411 between the locking cam and the locking wall, in order toovercome the resilience of the small spring 30. The torque of smallspring 30 has to be of a very low level, otherwise the string will notslide easy enough between the locking cam and the locking wall duringinstallation. The String will then be locked with an initial clampingstress by spring 30, if the spring itself is not yet tensioned. The beam3 can be mounted to the stringed instrument with screws or bolts 52through mounting holes 6 and 7. Preferably, the beam is positionedimmediately behind the top nut 50 of the stringed instrument (see FIG.8).

The beam 3 is preferably made from quenched quality steel, known underthe tradename: `RUS`, that can be quenched up to about 60 HRc. Thelocking cam is preferably made from rolled spring steel, class C, with aspecific hardness of circa 56 HRc. A possible production method is 2Delectro-erosive metal removing, although this method is ratherexpensive. A cheaper and quicker method is based on laser cutting, whichmethod also provides a better controllable surface condition. Inprinciple, it is possible also to laser cut the hole 22 for spring 30.Therefore, the laser-beam follows the contour of the locking cam andcuts in at slot s1 (FIG. 3) to make hole 22. This process is rathercomplex and not fully reliable because of the high local heatdevelopment. It is easier to pierce hole 22 with the laserbeam directlyinto the locking cam. In that case, slot s1, as shown in FIGS. 1,3,5 and6, is not present at all.

FIG. 2 shows appropriate dimensions for beam 3. The overall height h1is, for instance, 6 mm, while the height h2 of beam 3 underneath thechannels is, for instance, 4 mm. The height of the locking cams isdesigned in such a way, that it is a fraction lower than the height ofthe raised walls 41 . . . 48 to prevent the cams from being locked inbetween the beam 3 and a cover 51 (FIG. 8) being placed over it. Thetolerance between the locking cams and the cover 51 has to be small suchthat even the string with the lightest gauge cannot slip underneath alocking cam during the installation of the string or afterwards. Thewidth b1 of each channel at a locking cam 2 measures approximately 5.5mm, while the width b2 of a complete channel measures 7.5 mm. This widthb2 corresponds with the standard spacing between two adjacent strings ofa steel string guitar. When these dimensions are used, which providebeam 3 with sufficient stiffness, then a symmetrical design of beam 3,which is not allowed to be wider than the neck of the stringedinstrument, for instance, an electric guitar, would not leave enoughspace for a channel at one of the sides of the beam 3. In order toprevent beam 3 from protruding from the neck of the stringed instrumenta design is chosen for one of the ends of beam 3, as shown in FIG. 1.The locking cams 26, 27 on the right hand side of FIG. 1 each rotate intheir own wall 46, 47 measuring only half of the length of the otherwalls 41-45, 48. It is observed that the right hand side locking cam 27therefore is placed reversely in the channel related to the otherlocking cams 20, 23-26, concerning both the position of the rotationpoint and the position of its top and bottom surface.

FIG. 3 shows a top view of the locking cam in more detail. The lockingcam 20 can rotate about rotation point 21 having centre 211. Thedistance between centre 211 and the edge of the locking cam with whichthe string is being locked, depends on the angle φ and is indicated withr(φ). Furthermore, the curve of r(φ) depends on the type of string thathas to be locked. The fact is, it is found that the relationship of thedimensions of the eccentric for a wound string are preferably chosendifferent from the dimensions for plain strings. When, for instance, ina guitar, three plain strings and three wound strings are applied, thenthree eccentrics for plain strings and three eccentrics for woundstrings are applied. For a wound string the dimension rb, i.e. r(φ) withφ=0, is 5.5 mm. The dimension re, i.e. r(φ) for φ a little over π/2,measures in that case 4.0 mm. Slot s1, when present, measures less than0.2 mm. The distance s2 between slot s1 and the centre 211 measures 3.0mm. Radius r1 of the rotation point measures 1.0 mm, while the width ofopening 22 is 0.5 mm. Finally, the dimension of s3 measures 1.0 mm.These dimensions are applied for wound strings. For a plain string,radius re is preferably 4.75 mm, the other dimensions being equal tothose of the locking cam for wound strings.

FIG. 5 shows a top view of a locking cam for plain strings, referred toas p-type locking cam, while FIG. 6 shows a top view of a locking camfor wound strings, referred to as w-type locking cam. The curvature ofboth eccentrics is different, as explained above. In a preferredembodiment of both eccentrics the points a to t follow the coordinates,as shown in table 1. In both cases point a is chosen as origin.

FIG. 7 shows how the value of locking force Fk on the string depends onthe position P where the string S is locked between the locking cam andthe locking wall. Point O is for instance equal to the centre 211 ofrotation point 21 of locking cam 20. The line connecting points O and Pmakes an angle β to the line through O perpendicular to the locking walland, consequently, to string S. When the string is loaded with a tensionFs, it corresponds with said locking force Fk according to the followingformula:

    F.sub.k =F.sub.m /tan β

By choosing a small angle β, the locking force can be increased to anextremely high extent.

FIG. 4 shows a bottom view of beam 3, with the cavities 31 for thesprings 30 and the openings 6 and 7 for the mounting means clearlyvisible, whereas FIG. 8 shows where the locking apparatus according tothe invention is placed on guitar neck 54.

FIG. 8 shows the guitar neck 54 with six strings 53. Immediately behindtop nut 50 the locking apparatus 1 is placed, locking six strings 53. Acover-guiding plate 51 is provided to cover locking apparatus 1. Sixguiding slots 55 are provided in cover-guiding plate 51, one for eachstring 53, and two holes for the mounting screws or bolts 52 areprovided, with which mounting screws 52 the locking apparatus includingthe cover-guiding plate 51 is fixed to the guitar neck 54.

                  TABLE 1                                                         ______________________________________                                        Coordinates of a locking cam type W and type P                                (in mm relative to origin a)                                                         locking cam       locking cam                                                 type `W`:         type `P`:                                                   X:   Y:           X:     Y:                                            ______________________________________                                        a        0.0    0.0          0.0  0.0                                         b        0.101  0.472        0.061                                                                              0.476                                       c        0.241  0.927        0.162                                                                              0.941                                       d        0.419  1.361        0.303                                                                              1.391                                       e        0.632  1.772        0.482                                                                              1.825                                       f        0.878  2.155        0.696                                                                              2.238                                       g        1.153  2.510        0.944                                                                              2.628                                       h        1.453  2.833        1.223                                                                              2.992                                       i        1.777  3.124        1.531                                                                              3.327                                       j        2.120  3.380        1.864                                                                              3.632                                       k        2.479  3.600        2.221                                                                              3.904                                       l        2.850  3.784        2.596                                                                              4.142                                       m        3.230  3.932        2.988                                                                              4.345                                       n        3.615  4.042        3.393                                                                              4.510                                       o        4.000  4.116        3.808                                                                              4.639                                       p        4.387  4.153        4.229                                                                              4.730                                       q        4.768  4.153        4.653                                                                              4.783                                       r        5.139  4.124        5.077                                                                              4.798                                       s        5.500  4.060        5.497                                                                              4.777                                       t        5.847  3.965        5.911                                                                              4.732                                       ______________________________________                                    

FIGS. 11 and 12 show, that the locking cams 20, 23-27 do not necessarilyhave to be positioned parallel to the top plane of beam 3. They may, forinstance, also be positioned with an angle of about 90° relative to beam3 and, consequently, also relative to neck 54 of a guitar. In this casethe U-shaped channel in which the locking cam 20 is placed, is rotated90° relative to the designs according to the preceding figures. Thestring s in the design according to FIG. 10, after being placed betweenlocking cam 20 and locking wall 411, can be tightened by pulling theloose end of the string (in the figure at the right from beam 3) awayfrom the guitar neck 54. This is also valid for the other strings aswell. Consequently, the advantage is provided, that a headstock 64 canbe attached to the guitar neck 54, which is optically preferred above aguitar neck without a headstock. With the locking apparatus 1 accordingto the preceding figures the strings have to be tightened by pullingthem towards the bottom of beam 3, which can be seen referring to FIG.8. Therefore, in that design a headstock is not possible.

FIG. 12 shows a cross section along the line XII--XII in FIG. 11alongside locking cam 25. Between two adjacent locking cams, 20/23,24/25, 26/27, each time one appropriately wound spring 65 can beprovided, which, for instance, is anchored to the beam 3 with a bolt 66and has two loose ends. Each end is connected to one locking cam, sothat each spring 65 can push subsequently two locking cams 20/23, 24/25,26/27 with an appropriate load towards locking wall 411.

I claim:
 1. String locking apparatus of a stringed instrument, whichalso includes a tuning means for a string, which locking apparatusincludes a locking cam arranged about a point of rotation and a lockingwall, which locking cam and locking wall are positioned relative to eachother in such a way, that a string can be locked between them,characterized in that the rotatably arranged locking cam is an eccentricfrom a hard and stiff material, placed in a U-shaped channel beingfreely accessible from one side and provided in a hard and stiff beam,which channel includes the locking wall, a small spring being providedholding the locking cam to the locking wall in case no string is presentbetween the locking wall and the locking cam, and the eccentric isshaped in such a way that the locking cam and the locking wall contactat only one point in case there is no string in the channel.
 2. Stringlocking apparatus according to claim 1, characterized in that the beamincludes further U-shaped channels, one for each string of the stringedinstrument, and furthermore each channel includes its own locking camand locking wall, so that for each string a locking apparatus ispresent.
 3. String locking apparatus according to claim 1, characterizedin that the beam is placed directly behind the top nut of a guitar. 4.String locking apparatus according to claim 1, characterized in that thelocking wall of the U-shaped channel (channels) has a bevelled edge. 5.String locking apparatus according to claim 1, characterized in that thelocking cam each have an opening (22) for fixation of the spring of eachof the locking cams.
 6. String locking apparatus according to claim 5,characterized in that the beam in each channel is provided with a cavityunderneath each of the locking cams, so that the spring (30) for eachlocking cam can be completely inserted.
 7. String locking apparatusaccording to claim 1, characterized in that the spring for each lockingcam has a limited torque.
 8. String locking apparatus according to claim1, characterized in that the curvature of the eccentric depends on thetype of string (plain or wound) that has to be locked by it.
 9. Stringlocking apparatus according to claim 1, characterized in that thelocking cams are oriented substantially vertical relative to the beam.10. String locking apparatus according to any of the preceding claims,characterized in that the locking cam is laser cut from spring steel.11. String locking apparatus according to claim 1, characterized in thatthe beam is provided with one or two U-shaped channels, the beam beingmade from quench quality steel RUS and being quenched to approximately60 HRc.
 12. String locking apparatus according to claim 1, characterizedin that the beam is provided with one or two U-shaped channels the beambeing dimensioned in such a way that the distance between the channelscorresponds with the standard spacing between the strings of thestringed instrument and the length of the beam does not exceed the widthof the neck of the stringed instrument, to which the beam is mounted.13. Stringed instrument including a string locking apparatus accordingto claim 1 and at the same time provided with a tremolo, fixed to theother side of the strings opposite the side anchored to the lockingapparatus.